This invention relates in general to impact printers and, more particularly, it relates to impact printers wherein a ribbon moves between a ribbon storage area and a print point to continuously supply fresh ribbon to a position between a character element and a print receiving medium.
In some printers of this type including typewriters, the ribbon storage has been provided by a cartridge. These cartridges are removable so as to permit the ribbon supply to be replenished by merely replacing the ribbon cartridge. Prior art ribbon cartridges typically comprise a supply reel and a take-up reel situated within a housing. Ribbon from the supply reel emerges from the housing and is positioned at the print point. The print point is situated between a character element and the print receiving medium. From the print point, the ribbon returns to the housing where it is stored on a take-up reel.
However, in some prior art impact printers, when the operator desired to change the ribbon cartridge, it was necessary to thread the ribbon around guides which keep the ribbon in the vicinity of the print point and also to thread it through lifters which raise and lower the ribbon each time a character is printed. This threading of the ribbon is time consuming for the operator of the printer and it also presents some risk that the print receiving medium may be in some way defaced by removing and replacing the cartridge, e.g., smearing is not at all uncommon in such circumstances. Further, where the printing medium or ink is of the correctable or lift-off type, the ink may be easily disturbed when the ribbon is threaded so as to impair the printing operation.
Further, in various printers including typewriters such as those manufactured by IBM and SCM, the platen which supports the print receiving medium in the impact printing position remains stationary and the character printing elements move along the platen to the various printing locations. In these printers the ribbon cartridge has been mounted for movement with the character elements and the print point so as to continuously supply fresh ribbon to the print point as the character elements advance. Typically, the cartridge has been supported on a carriage which moves linearly along the platen. The character elements may be transported on the carriage or may be mounted on a ball or wheel oftentimes referred to as a daisy. In some of these type printers, it has been necessary for the operator to remove the ball or daisy when the ribbon cartridge was changed. The removal of the daisy thus increased the time required for the operator to change the cartridge. Further, even if the character element is not removed, it is still necessary to thread the ribbon around the guides and lifters near the print point.
To a certain extent in printers having moving print points the problem of positioning the ribbon has been solved by means of a rigid member connected to the cartridge. The member grasps the ribbon and aligns it near the print point. However, in copending applications Ser. No. 833,270, filed Sept. 14, 1977 in the name of Dan W. Matthias, and Ser. No. 833,257, filed Sept. 14, 1977 in the name of Dan W. Matthias and Collier M. Miller, assigned to the assignee of this invention, it is disclosed that it may be desirable to support the ribbon cartridge in a stationary position and to supply ribbon to a print point movable with respect to the cartridge by means of two flexible leaders which provide a ribbon path of fixed length from the cartridge to the print point and back again to the cartridge. With this type of cartridge, it is necessary to thread the ribbon emanating from the leaders around the guides and lifters near the print point and when the print point is movable with respect to the cartridge, it is not possible to guide the ribbon with a rigid member affixed to the cartridge.